Method and reagent for surface polishing



United States Patent 3,385,682 METHOD AND REAGENT FOR SURFACE POLISHING Jack Lowen, Williamstown, Mass, assignor to Sprague Electric Company, North Adams, Mass 'a corporation of Massachusetts No Drawing. Filed Apr. 29, 1965, Ser. No. 451,995

2 Claims. (Cl. 51293) ABSTRACT OF THE DISCLOSURE A semiconductor polishing composition and process comprising applying to a semiconductor a carrying agent, a complexing agent, an oxidizing agent, and an abrasive material.

This invention relates to a meth d and reagent for polishing and preparing semiconductors, metals, and other materials for use in the electronics industry.

Semiconductors or other materials used in the electronics industry must have a smooth surface to effectively operate in their intended manner particularly in the latest planar structures. At present, many methods involving mechanical polishing or chemical polishing are employed with varying degrees of success to obtain the desired surface smoothness. These methods, however, are usually either too time consuming or too ineflicient or yield surfaces marked by viscous fluid flow patterns.

An object of this invention is to provide a method and reagent for effectively polishing and preparing the surface of semiconductor crystals, combining the advantages of chemical and mechanical polishing.

In general, the reagent used in the method of this invention includes a c mplexing agent that can chelate with the material being polished, an oxidizing agent that can react with the material and an abrasive powder which are incorporated in a slurry using water or other media as a carrying agent. The slurry is applied to the material in a mechanical polisher such as Bausch & Lomb No. 2l-1l86 enclosed in an air-tight box under a positive pressure of filtered air or inert gas such as nitrogen. A Sterilshield enclosure made by Baker is particularly effective.

The mechanical polisher used can be any standard mechanical polisher such as Bausch & Lomb No. 21-11-86 or Buehler Polishers or the new vibromatics put out by Fisher or Buehler. Prior to the polishing procedure a lapping schedule to remove all deformation caused by slicing or machining is essential. Regardless of how carefully the mechanical polishing operations are carried out, some surface deformation will remain. The incorporation of an active reagent to react with the material and a complexing agent to hold it in solution along with the usual abrasive slurry has a number of important advantages over either mechanical or chemical polishing:

(1) It is faster than mechanical polishing. Using Versene and peroxide reduces the time necessary to pOlish silicon from about four hours to about one and one-half hours.

(2) Since the action is chemical as well as mechanical, the material abraded from the specimen reacts with the reagent and does not fill in scratches and imperfecti ns on the surface as in mechanical polishing. A polished surface as produced by this method will have less surface damage than a mechanically polished surface.

(3) Since the action is mechanical as well as chemical, the sample is not marked by swirling patterns of hydraulic flow and the edges are not rounded to any significant dimension. The solutions used are not as corrosive or toxic and therefore safer for routine use.

The reagent of this invention is particularly effective 3,385,682 Patented May 28, 1968 for polishing silicon, gallium-arsenide, germanium, and other semiconductors. The reagent or slurry of this invention attacks the surface to increase the rate of polishing, and dissolves the particles abraded from the material being polished to reduce abrasion and surface damage. Ordinarily, the polishing involves a surface smearing or film to cover and fill in surface damage. The slurry of this invention dissolves this film and produces a comparatively damage free surface.

The complexing agent used in the slurry may advantageously be selected from the following group:

Versene chloride fluoride citrate tartrate cyanide oxalate mannitol The oxidizing agent used in the slurry may advantageously be selected from the following group:

peroxide nitrate perchlorate persulfate (a) complexing agent, 8 to 20% by weight (b) oxidizing agent, 1 to 10% by weight (c) abrasive, 20 to -g./250 ml. of slurry The following are examples of specific applications of this invention:

Example 1 Silicon or gallium arsenide is used as the semic nductor. The slurry contains the following components: one pound Versene (the tetrasodium salt of ethylene diamine tetra acetic acid) per gal. of H 0; approximately 3% of H 0 i.e. 2030 cc. of 30% per 250 ml. charge of slurry and 50-60 g. of Linde metallurgical Grade High Purity Alumina Abrasive.

Example 2.

Silicon is polished using 10 g. NaF, 5 g. NaOH, 50 ml. H 0 g. of Linde Metallurgical Grade Alumina and 25 ml. glycerine in 425 ml. H O.

It is to be understood that the invention is not limited to the specific examples indicated above. For example, 5% KNO 5% KCl and 10% mannitol in a slurry containing 20% of Linde Metallurgical Grade Alumina can be used to polish germanium.

Since it is obvious that many changes and modifications can be made without departing from the nature and spirit of the invention, it is to be understood that the invention is not limited to the above description except as set forth in the appended claims.

What is claimed is:

1. A reagent slurry for surface polishing a semiconductor consisting essentially of from 8 to 20% by weight of a member of the group consisting of the tetrasodium salt of ethylene diamine tetra acetic acid, sodium fluoride and mannitol; 1 to 10% by weight of a member of the group consisting of hydrogen peroxide and potassium nitrate; a carrying agent selected from the group consisting of water and a water and glycerine mixture; and from 3 4 20 to 80 g./250 ml. of slurry of a hard abrasive selected 2,294,760 9/1942 Morris 51-307 from the group consisting of aluminum oxide, cerium xide 2,683,343 7/ 1954 Gillette et a1 51-304 and diamond dust. 3,103,733 9/1963 Fauro et a] 204143 2. A method of polishing the surface of a semicon- 3,158,517 11/1964 Schwarzenberger 252-793 X ductor comprising applying the composition of claim 1 to 5 3,228,816 1/1966 Kendall 204-140.5 the surface of said semiconductor While maintaining rela- 3,248,235 4/ 1966 Pryor et al 51-304 21;; motion between sa1d semiconductor and said compo- OTHER REFERENCES References Cited Camp, A Study of the Etching Rate of Single-Crystal Germanium, Journal of Electro-Chem. Society, vol. 102, UNITED STATES PATENTS 10 Nov. 10, 1955, pp 1,800,881 4/1931 Andrus et a1. 106-14 2,082,950 6/ 1937 Green 106-14 DONALD J. ARNOLD, Primary Examiner. 

